No Link Between Diabetes and Knee Osteoarthritis

Also no association between fasting glucose or insulin resistance

Diabetes and markers of abnormal glucose metabolism were not associated with an increased risk for incident knee osteoarthritis (OA), a prospective study found.

After adjustment for sex, age, race, clinic site, and body mass index (BMI), there was no significant association between having diabetes at baseline and the development of knee OA over 7 years of follow-up (OR 0.79, 95% CI 0.53-1.18, P=0.246), according to Tara S. Rogers-Soeder, PhD, of the University of California Davis School of Medicine in Sacramento, and colleagues.

Diabetes and OA are both common among older individuals, with an estimated 25.9% of adults 65 and older having diabetes and 35% of obese adults ages 60 to 64 having knee OA.

Some previous studies and meta-analyses have suggested a link between diabetes and OA, but were limited by using different methods of diagnosing OA, failing to adjust for BMI, or combining knee, hip, and hand OA. Moreover, a recent systematic review of five studies that did adjust for obesity found no association between abnormal glucose metabolism and OA in three studies, an increased risk in one, and a decreased risk in another.

To more clearly determine whether there is an association between diabetes and knee OA, the researchers analyzed data from the Multicenter Osteoarthritis Study (MOST), which is a National Institutes of Health–funded longitudinal cohort study of risk factors for knee OA. It includes more than 3,000 individuals ages 50 to 79 who have, or are at risk for, knee OA. The clinical centers for the study are at the University of Alabama at Birmingham and the University of Iowa.

The analysis included 987 individuals without knee OA at baseline. Their mean age was 61, 58% were women, and mean BMI was 29.1 kg/m2. A total of 9.5% had diabetes at baseline, and those patients were more likely to be men, non-white, and residents of Alabama.

Among the Alabama group, the prevalence of diabetes in whites was 8.4% (10.1% in men and 7.2% in women), while the prevalence among blacks was 23.3% (31.5% in men and 16.7% in women). In the Iowa group, the prevalence of diabetes for whites was 7.1% (9% in men and 5.8% in women).

Of the 94 patients with diabetes at baseline, 56 were taking diabetic medications, including 42 who were using metformin.

The analysis included 1,972 knees, of which 409 developed incident OA. By the end of follow-up, at 84 months, the cumulative incidence of knee OA was 23.3%.

In an unadjusted model, there were significant associations between fasting glucose (OR 1.14, 95% CI 1.02-1.28, P=0.021) and HOMA-IR (OR 1.13, 95% CI 1.01-1.27, P=0.033) and knee OA. Similarly, in a model that adjusted only for sex, age, race, and clinic site, increased risks were seen for fasting glucose (OR 1.14, 95% CI 1.01-1.27, P=0.031) and HOMA-IR (OR 1.13, 95% CI 1-1.27, P=0.042). However, with further adjustment for BMI, statistical significance was lost.

There was a significant association for HOMA-IR with stratification by sex. For women, an elevation of HOMA-IR was associated with a decreased likelihood of incident knee OA (OR 0.80, 95% CI 0.69-0.94, P=0.005), whereas no association was seen for men (OR 1.09, 95% CI 0.89-1.33, P=0.424).

"Our observation of an inverse association between HOMA-IR and odds of radiographic knee OA incidence in women was unexpected and possibly spurious but was not explained by use of diabetic medications or metformin in particular, in those with insulin resistance," Rogers-Soeder and colleagues wrote. They indicated that further research into protective effects of diabetic medications is warranted.

Limitations of the study included the inclusion of only tibiofemoral OA and only patients at elevated risk for OA, so the results may not have full generalizability.

"Contrary to our hypothesis, after adjustment for BMI (a strong risk factor for both diabetes mellitus and knee OA) we did not find increased odds of incident radiographic knee OA in participants with diabetes mellitus nor in participants with higher baseline levels of fasting glucose and HOMA-IR," they concluded.

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